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Engine Controls - Pin Voltage Charts: Introduction

Pin voltage charts are supplied to reduce diagnostic time. Checking pin voltages at the DME/Motronic control unit determines whether it is receiving and transmitting proper voltage signals. Charts may also help determine if control unit wiring harness is shorted or opened.

NOTE: Unless stated otherwise in testing procedures, perform all voltage tests using a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance. Voltage readings may vary slightly due to battery condition or charging rate.
DME/MOTRONIC CONTROL UNIT PIN ASSIGNMENTS (1) (318i & 318is - 1.8L M42 ENGINE; DME 1.7)

Pin No. Function/Description Signal Type Or Voltage Value
1 Fuel Pump Relay (2) Ground Signal Term. 85
3 Fuel Injectors (No. 2 & 4) Square Wave Output Signal
6 Fuel Injectors (Ground) Ground Circuit
8 CHECK ENGINE Light (3) Ground Circuit (Output Signal)
11 Potentiometer Signal Electronic Transmission Control (EGS) Output Signal
12 Throttle Potentiometer (TPS) (4) 5 Volts (Input Signal)
14 Airflow Sensor Ground Circuit
15 Knock Sensor (No. 1 & 2) Sensor Input
16 Camshaft Sensor Square Wave Input Signal
17 Instrument Cluster (Tach Signal) Square Wave Output Signal
18 Intake Air Changeover Valve Ground Circuit (Output Signal)
24 Ignition (Cylinder No. 3) Primary Circuit Output Signal
25 Ignition (Cylinder No. 1) Primary Circuit Output Signal
26 Battery Voltage (Permanent) 12 Volts (Battery Voltage Input)
27 DME Master Relay Ground Circuit
28 Sensors (Shield Wire) Ground Circuit
29 Idle Speed Control Square Wave Output Signal
32 Fuel Injectors (No. 1 & 3) Square Wave Output Signal
34 Ground (Except Injectors & Ignition) Ground Circuit
36 Fuel Tank Vent (Evaporation) Control Ground Circuit (If Open)
37 Oxygen Sensor Heater Relay Ground Circuit (If Heating Element Is On)
41 Airflow Sensor Zero Volt (Input Signal)
42 Knock Sensor (No. 3 & 4) Sensor Input
43 Engine Sensors Ground Ground Circuit
44 Camshaft Position Sensor Sensor Input Circuit
48 A/C Compressor Cut-Off (5) Compressor Relay Term. 85
51 Ignition (Cylinder No. 4) Primary Circuit Output Signal
52 Ignition (Cylinder No. 2) Primary Circuit Output Signal
54 Battery Voltage 12 Volts (Battery Voltage Input)
55 Ignition (Ground) Ground Circuit
56 Start (Ignition) Input 12 Volts (Battery Voltage Input)
59 Airflow & Throttle Position Sensors 5-Volt (Reference) Output Signal
60 Programming Voltage (6) Ground Circuit (Input Signal)
64 Ignition Timing Intervention Transmission Module Circuit (Input Signal)
65 Park/Neutral Switch (7) Ground Circuit (Input Signal)
67 Crankshaft Position Sensor Square Wave Input Signal (Inductive)
68 Crankshaft Position Sensor Ground Circuit (Inductive)
70 Oxygen Sensor 0.2-0.8 Volt (Input Signal)
71 Oxygen Sensor (Ground) Ground Circuit
73 Speedometer Signal Square Wave Input Signal
74 Engine Speed (TD) Signal Square Wave Output Signal
76 Airflow Sensor Input Signal
77 Intake Air Temp. Sensor Zero Volt (Input Signal)
78 Engine (Coolant) Temp. Sensor Zero Volt (Input Signal)
81 Anti-Theft Alarm Switch (8) 12 Volts (Battery Voltage Input)
85 A/C Compressor (9) 12 Volts (Battery Voltage Input)
86 A/C Switch (10) 12 Volts (Battery Voltage Input)
87 Diagnostic Initiation Line (RxD) 12 Volts (Battery Voltage Input)
88 Diagnostic Data Line (TxD) Ground Circuit (Input/Output Signal)
(1) Pin assignments not listed are not used (blank).
(2) Ground output signal from control unit.
(3) If exhaust relevant fault stored in memory.
(4) Five-volt signal input to control unit will vary depending on throttle position.
(5) At 5 MPH and engine at full load.
(6) With diagnostic socket cover closed.
(7) In Park or Neutral position.
(8) With anti-theft alarm activated (armed).
(9) With A/C compressor clutch engaged.
(10) With A/C system on.
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